Sharp EL-5100

The Sharp EL-5100 is a vintage calculator with formula storage. Up to 5 simple algebraic formulae (80 steps in total length) can be stored and executed. The machine offers no branching or conditionals, so loops or iterative programs cannot be entered. Nevertheless, it's quite an interesting and useful beast; the one I just received was obviously much loved by its previous owner.

I have not yet tried shoehorning my favorite example, the Gamma function into this calculator's formula memory; thanks to ten registers that can be used to store constants, it just might be possible to enter an expression of that complexity. For now, here's an improved version of Stirling's formula, one which provides a very good approximation of the Gamma function for large arguments (and a reasonable approximation for small ones):